Control device



Patentei sept. 23, 1941 CONTROL DEVICE George T. McDonald, Minneapolis,Minn., as-

signor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., acorporation of Delaware Application April 18, 1938, Serial No. 202,609

(Cl. 2in-62) 6 Claims.

ThisI invention relates to electrical resistance and switching apparatusadapted to vary the resistance in an electrical circuit or direct anelectric current into different paths.

Electrical apparatus of this type usually has an electrical resistanceelement or a series of contacts over which a movable contactmechanically frictionally slides. In such devices there is considerableelectrical resistance between the movable contact and the resistanceelement or stationary contacts which is known as contact resistance.This contact resistance ls different for different positions of themovable contact. It also changes from time to time for the same positionVbecause dust and other foreign particles get under the contact and alsobecause the contacts and resistance element tend to corrode with age.There is also a tendency for the contacts and resistance to burn and pitbecause of a poor contact and thus further increase the resistance.'I'his contact resistance is very detrimental to the life and accuracyof such apparatus.

When such devices are operated manually or where a large amount of poweris available for operating them, a heavy contact pressure may be usedand, as a result, the contact resistance does not seriously affect theiraccuracy or usefulness. However, when they are operated automatically bythermostats and other such devices which produce a very small amount ofpower. they are not satisfactory. If a heavy contact pressure is used toovercome the detrimental contact resistance, then they do not readilyrespond to the automatic means and are therefore unsatisfactory. If alight contact pressure is used to make them readily respond to theautomatic means the contact resistance becomes quite large and seriouslyinterferes with the accuracy and usefulness of the device. This lightcontact pressure makes it easy for dust and other foreign particles toget under the contact and cause burning and pitting of both the movablecontact and the resistance or the stationary contacts which additionallyincreases the contact resistance.

It may be desirable to locate such a control device in place where thesurrounding atmosphere contains combustible gas, vapor or dust. An opencontact resistance or switching mechanism is dangerous because somearcing-is likely to occur as the contact is moved. A

An object of this invention is to provide an improved variableresistance or contact mechanism which vcan be successfully operatedautomatically with a minimum of power.

tending outside the envelope Il.

Another object is to provide a variable resistance or a contactmechanism which has a low contact resistance that does not change withage.

Another object is to provide a variable resistance or contact mechanismin which the movable contact moves over the resistance or contacts inresponse to variations in a magnetic eld.

Another object is izo-provide an electrical contact mechanism having thecontacts hermetically sealed.

Another object is to provide an electrical contact mechanism having thecontacts hermetically sealed and in which a magnetic ileld varied bymeans outside the sealed space actuates the contacting device within thesealed space.

Another object is to provide a variable resistance or contact mechanismin which all electrical contacts are made and broken 'within anhermetically sealed chamber to eliminate the possibility of ignitingcombustibles in the vicinity of the device.

Other objects will be evident from the .appended claims, specificationand from the drawing, in which:

Figure 1 is a horizontal section of one form of the invention.

Figure 2 is a vertical section taken on line 2-2 of Figure 1.

Figure 3 is a horizontal section of another form of the invention.

Figure 4 is a vertical section taken substantially on line I-l of Figure3.

Figure 5 is a horizontal section of a third form of the invention.

Figure 6 is a vertical section taken on line 6-6 of Figure 5.

Figure 7 -is a horizontal section of a fourth form of the invention.

Figure 8 is a vertical section taken substantially on line 8 8 of Figure7.

Throughout the various modifications of the invention here described,like reference characters are used to indicate corresponding parts.

In the device shown in Figures l and 2, an electrical resistance IU inthe form of a potentiometer is horizontally disposed within a sealedglass envelope Il. The left-hand end of the resistance i0 is providedwith a lead wire I2 extending outside the glass envelope Il and sealedtherein. The right-hand end of resistance I0 is similarly provided witha lead wire I3. Parallel to resistance i0 but horizontally spacedtherefrom within envelope Il ls a conducting bar Il which is alsoprovided with a lead wire I5 ex- Insulating blocks I6 and Il serve asspacers and supports for resistance I and bar I4. l

In order to vary the effective value of resistance I0 an electricallyconducting roller I6 is provided to bridge resistance I 0 and bar I4.Between resistance I0 and bar I4, roller Il is provided with an annulariron or steel armature I9. Armature I9 is suitably spaced from roller I8as by insulation 20. The roller could be constructed in any way thatwould provide an electrical connection between resistance I0 and bar I4together with an armature coaxially disposed with relation to theroller.

The envelope I I serves the purpose of keeping dust and dirt off theworking parts, of preventing corrosion of the contact surfaces, assuringuniform operation, and of preventing arcing at the contact from ignitingany combustibles in the vicinity of the device.

A permanent magnet 2| outside the glass envelope may be moved lengthwisethereof by any suitable means, not shown, such as a temperatureresponsive element. Since the armature I9 will be included in the fieldof magnet 2I it will move the roller I8 along the resistance and bar onchanges in position of the magnet with respect to the envelope. Sincethere are no sliding contacts, very little effort will be required tochange the effective value of the resistance. Good contact is assuredbecause the contact surfaces will not corrode or become dirty.

The device shown in Figures 3 and 4 is similar to that shown in Figures1 and 2 except that a segmented contact member 23 is substituted for theresistance element. Contact member 23 consists of alternate segments ofnon-magnetic metal and insulation arranged diagonally of the length ofthe member, By providing member 23 with a fiat upper surface and thediagonal contact segments, the roller I8 will never be in open circuitposition. If open circuit positions of the roller are desired, thesegments could be straight rather than diagonal. 'I'he segments areprovided with separate lead wires 24 extending through the glassenvelope.

The operation of this modification of the invention is similar yto thatof the preceding modication, except that the roller completes anelectrical circuit between bar I4 and the various segments of contactmember 23 rather than between the bar and the windings of an electricalresistance. An external resistance may have taps leading to theterminals 24 or the device may be used for any purpose where it isdesired to selectively control a plurality of electric circuits.

It should be particularly pointed out in connection with these first twomodifications that the construction including a rotating armaturematerially increases the sensitivity of the device. Bearing in mind thatthere is necessarily some mechanical resistance to moving roller I8along the two parallel conductors in either the first or secondmodification, it will be understood that magnet 2| must be displacedfrom a point immediately beneath armature I9 before the horizontalcomponent of force along the length of the conductors will be sufficientto move armature I6 and roller I8. Here, however, a slight movement ofmagnet 2| in one direction will result in a greater magnetic pull beingexerted on that portion of the armature which will move toward themagnet when movement of the armature is accomplished but which isslightly elevated until there is a movement. The increased pull on thisportion of the armature exerts a torque on the roller I8 whichinstigates movement before it would otherwise occur.

The device shown in Figures 5 and 6 is similar to the device of Figures1 and 2 except that a globule of mercury 25 is substituted for theroller- I8 as the movable contact member. As in the previousmodifications the bar I4 and the resistance I0 is horizontal when inoperative position. Here, however, the bottom of the glass envelope IImust also be horizontal so that the globule of mercury 25 will not tendto move of its own weight. In order to move the globule of mercury 25, aspool-shaped armature 26 is placed over the mercury with its twoenlarged ends confining the mercury lengthwise of the envelope Il.Because of the high surface tension of mercury, movements of thearmature 26 will cause the globule 25 to move correspondingly. Thedensity of mercury is so great that it will tend to float the steel oriron armature reducing friction between the armature 26 and envelope IIto a minimum. It has been found desirable to coat the armature 26 withvitreous enamel to serve as electrical insulation, preventing electricalcontact of either bar Il or resistance I0 by the armature, and to givethe armature a very smooth surface. Magnet 2I serves to move thearmature and mercury in this case as it did to move the roller in theprevious cases.

In Figures 7 and 8 a segmented contact member as employed in Figures 3and 4 is substituted for the resistance element of Figures 5 and 6. Itis not necessary, here, to provide diagonal segments as in Figures 3 and4 in order to avoid open contact positions of the movable contactbecause mercury 25 makes contact along an appreciable length of contactmember 23. As described in connection with the previous modifications,movements of magnet 2I lengthwise of envelope II serves to move themercury to bridge bar Il and contact member 23 at various points alongtheir length.

While the several modifications have been described as employing a glassenvelope Il, it will be seen that any suitable non-magnetic material maybe used. If a metal envelope were used it would be possible to eliminateconducting bar Il by using the envelope as a conductor in place of thebar. In that case lead wires t the resistance or segmented contactmember would necessarily be insulated from the envelope.

It will be seen from the foregoing specification that a variableresistance or contact mechanism has been provided that may be operatedwith a minimum of power, one that has low contact resistance which willremain constant over a long period of time, and one that will notpresent a fire hazard in certain installations.

While several modifications of the invention have been described, othermodifications will be apparent to those skilled in the art. Theinvention should be limited only by the appended claims.

I claim as my invention:`

1. In a current controlling device, the combination of, an elongatedhorizontally located tubular container of non-magnetic material, a pairof elongated contact members hermetically sealed therein and locatedlengthwise in parallel relation in the container, contacting meansbridging the elongated contact members and adapted to be moved along thesame, at least one of said contact members being of the type used tovary the electrical resistance of a circuit in accordance with the pointat which said member able longitudinally thereof for magnetically movingthe armature and hence the contacting means along the elongated contactmembers.

2. In a current controlling device, the combination of, an elongatedhorizontally located container oi non-magnetic material, a pair ofelongated contact members hermetically sealed therein and locatedlengthwise in parallel relation in the container, rollable meanssupported by the two elongated contact members and adapted to be movedalong the same for bridging them electrically at various proportionsoftheir lengths. at least one of said contact members being of the typeused to vary the electrical resistance o! a circuit in accordance withthe point at which said member is contacted, an armature in thecontainer and located between the elongated con-n tact members formoving the rollable means along the contact members, and a magnetoutside of the container movable longitudinally thereof for magneticallymoving the armature and hence the rollable means along the elongatedcontact members.

3. In a current controlling device, the combination of, an elongatedhorizontally located container of non-magnetic material, a pair ofelongated contact members hermetically sealed therein and locatedlengthwise in parallel relation in the container, a globule of mercurybridging the elongated contact members and adapted to be moved along thesame, at least one of said contact members being of the type used tovary the electrical resistance of a circuit in accordanceK with thepoint at which said member is contacted, an'armature in the containerlocated between the elongated contact members to constrain the globuleof mercury lengthwise of the container for, positioning the globule atvarious points along the lengths of the contact members,

.and a magnet outside of the container movable relation in thecontainer, contacting means bridging the elongated contact members andadapted to be moved along the same, at least'one of said contact membersbeing of the typeused to v ary the electrical resistance of a circuit inaccordance with the point at which said member is contacted, an armaturein the container and located between the elongated contact members andclose to the surface of the container for moving the contacting meansalong the contact members, said armature being guided in itslongitudinal movement by said elongated contact members, and a magnetoutside of the container -and adjacent said armature, said magnet beingmovable longitudinally thereof for magnetically moving the armature andhence the contacting means along the elongated contact' members.

5. In a current controlling device, the combination of, an elongatedhorizontally located tubular container of non-magnetic material, a pairof elongated contact members hermetically sealed therein and locatedlengthwise in parallel relation in the container, contacting meansbridging the elongated contact members and adapted to be moved along thesame, at least one of said contact members being an electricalresistance, an armature in the container and located between theelongated contact members and close to the surface of the container formoving the contacting means along the contact members, and a magnetoutside of the container and adjacent said armature, said magnet beingmovable longitudinally thereof for magnetically moving the armature andhence the contacting means along the elongated contact members.

6. In a current controlling device, the combination of, an elongatedhorizontally located tubular container of non-magnetic material, a pairof elongated contact members hermetically sealed therein and locatedlengthwise in parallel relation in the container. contacting meansbridging the elongated contact members and adapted to be moved along thesame, at least one of said contact members being of the segmentedcontact type, an armature in the container and located between theelongated contact members and close to the surface of the container for.moving the contacting means along the contact members, and a magnetoutside of the container and adjacent said armature, said magnet beingmovable longitudinally thereof for magnetically moving the armature andhence the contacting means along the elongated contact members.

GEORGE T. MCDONALD.

